THE SKELETON AND TEETH.
Section A. The Skull.
IN the preceding chapter we saw how many of the external characters, which are employed by systematists for taxonomic purposes, vary considerably with age, sex and environment; and many of the data which were formerly regarded as specific characters are now regarded, at best, as characteristic of sub-species. These remarks also apply, but with even greater force, to the skull; for no structure is so influenced by physiological agents acting from within, or by physical agents operating from without. By physical agencies I mean those impressions which the environment brings to -bear on the surface of the body. It is, therefore, evident that the student should examine many skulls before he conies to definite conclusions as regards the cranial characters of each Anthropoid. Fortunately the skulls in our great Museums are provided with labels giving data of age, sex and the localities where they were found; so the student has ample material for thorough craniological investigations.
As age * advances the cranial and facial parts of the skull increase in size up to a point, but the latter continues to enlarge after the cranial part has stopped growing. In the Orang it keeps altering throughout